Syllabus Edition
First teaching 2021
Last exams 2024
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Basic Percentages (CIE IGCSE Maths: Extended)
Revision Note
Author
MarkExpertise
Maths
Basic Percentages
What is a percentage?
- “Per-cent” simply means “ ÷ 100” (or “out of 100”)
- You can think of a percentage as a standardised way of expressing a fraction – by always expressing it “out of 100”
- That means it is a useful way of comparing fractions e.g.
½ = = 50%
⅖ = = 40%
¾ = = 75%
How do I work out basic percentages of amounts?
- You can use simple equivalences to calculate percentages of amounts without a calculator
- 50% = so you can divide by 2
- 25% = so you can divide by 4
- 20% = so you can divide by 5
- 10% = so you can divide by 10
- 5% = so you can find 10% then divide by 2
- 1% = so you can divide by 100 etc.
- You can then build up more complicated percentages such as 17% = 10% + 5% + 2 x 1%
How do I find any percentage of an amount?
- Method 1: You can find any percentage of an amount by dividing by 100 and multiplying by the given %
- 23% of 40 is 40 ÷ 100 = 0.4, multiply by 23: 0.4 × 23 = 9.2
- Method 2: To find “a percentage of X”: multiply X by the "decimal equivalent" of that percentage (percentage ÷ 100)
- for example, 23% of 40 is 40 x 0.23 = 9.2
- To find “A as a percentage of B”: do A ÷ B to get a decimal, then x 100, e.g.
- for example, to find 26 as a percentage of 40 first do 26 ÷ 40 = 0.65, then x 100 to get 65%
- 26 is 65% of 40
- for example, to find 26 as a percentage of 40 first do 26 ÷ 40 = 0.65, then x 100 to get 65%
Worked example
Jamal earns £1200 for a job he does and pays his agent £150 in commission.
Express his agent's commission as a percentage of Jamal's earnings.
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